CN111835205B - Sampling control circuit - Google Patents

Sampling control circuit Download PDF

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Publication number
CN111835205B
CN111835205B CN202010752623.XA CN202010752623A CN111835205B CN 111835205 B CN111835205 B CN 111835205B CN 202010752623 A CN202010752623 A CN 202010752623A CN 111835205 B CN111835205 B CN 111835205B
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circuit
sampling
synchronous rectification
resistor
transformer
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CN111835205A (en
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王志燊
马守栋
钟天明
何椿炜
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Mornsun Guangzhou Science and Technology Ltd
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Mornsun Guangzhou Science and Technology Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33592—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention discloses a sampling control circuit, which utilizes a switching power supply circuit with a synchronous rectification communication function to control the turn-off of a synchronous rectification tube by giving a narrow pulse to a power tube and simultaneously feed back an output voltage signal to a primary side, thereby solving the problem of low utilization rate of a magnetic isolation transformer in the conventional synchronous rectification signal transmission, simultaneously omitting a 431 circuit on a secondary side and reducing the board distribution area. The sampling control circuit of the invention combines the synchronous rectification control and the isolation sampling function, improves the utilization rate of the transformer, has good temperature characteristic, small occupied area and low cost.

Description

Sampling control circuit
Technical Field
The invention relates to a sampling control circuit of a switching power supply, in particular to a voltage isolation sampling control circuit of a flyback switching power supply with a synchronous rectification communication function.
Background
At present, in a switching power supply system, an optical coupler is often adopted as an isolation device to transmit an output voltage signal from a secondary side to a primary side, when the output voltage is low and the output current is large, a scheme of synchronous rectification is also needed, and an MOS (metal oxide semiconductor) tube with a low-pass resistance replaces a rectifier diode, so that the effect of improving the efficiency is achieved. In consideration of preventing the common situation of the primary and secondary power tubes, the need to disable the synchronous rectification function under the light-load working state is also considered to improve the efficiency, the primary and secondary control ICs are always required to be isolated and communicated, and the mode usually adopted is to use an air-core transformer to carry out isolated communication. The air core transformer is in addition to use the traditional isolation sampling circuit that isolator is the opto-coupler, owing to used two sets of isolator, and it is big to account for the face area, and is with high costs, and the opto-coupler has light intensity decay moreover, and radiation resistance is relatively poor, and the temperature floats great.
The circuit schematic diagram shown in fig. 1 is a traditional synchronous rectification flyback switching power supply circuit, a main power circuit comprises a transformer TX2 consisting of a primary winding P2 and a secondary winding S2, a main power MOS transistor Q4, a synchronous rectifier Q3 and an output filter capacitor C2, and the adopted voltage sampling feedback scheme is a common 431 circuit and an optocoupler. The conventional flyback switching power supply circuit with synchronous rectification has the following defects:
1. the voltage isolation sampling uses an optical coupler, and the optical coupler has the defects of light intensity attenuation and large temperature drift;
2. in order to ensure the precision of the voltage stabilizer, the 431 circuit is often arranged on the secondary side, so that the 431 circuit, the optocoupler and related peripheral devices occupy a large amount of PCB area, and the reduction of the size of the switching power supply is influenced;
3. the synchronous rectification isolation communication uses another isolation device, namely an air core transformer TX1, and because two sets of isolation devices are used, the utilization rate of the devices is low, the cost is high, and the occupied area of the device is large.
Disclosure of Invention
In view of this, the technical problem solved by the present invention is to overcome the deficiencies of the existing schemes, and provide a sampling control circuit, which does not need to use an optical coupler, and performs function multiplexing on a transformer, and uses the same transformer to transmit a voltage signal and a synchronous rectification signal, thereby reducing the volume and cost of a switching power supply, and in addition, a secondary side does not need 431 and a peripheral circuit thereof, thereby further reducing the volume and cost.
In a conventional synchronous rectification signal transmission scheme, only one pulse is generally transmitted, and a synchronous rectification on-off signal is transmitted through the pulse. In the traditional transmission scheme, only the edge information of the pulse is utilized, and the amplitude information of the pulse is not utilized, so that the utilization rate of the whole transmission transformer is not high.
In the invention, the characteristic that a diode and a capacitor can clamp the voltage is utilized, the voltage amplitude of the transmission transformer is clamped at the output voltage, and the scheme of utilizing the edge information of the pulse and the amplitude information of the pulse can be obtained by combining the conventional scheme.
The scheme can be used for the closed-loop control of any switching power supply circuit (including flyback, forward, asymmetric half-bridge flyback, LLC and the like) with a synchronous rectification communication function. For convenience of explanation, the description of the scheme is mainly performed on the flyback switching power supply circuit in the following.
The technical scheme of the invention is as follows:
a sampling control circuit is applied to a switching power supply circuit with a synchronous rectification communication function, and is characterized in that:
the port includes: the synchronous rectification circuit comprises a direct-current power supply input end VCC, a sampling output end Vs, a synchronous rectification signal input end BOS, a primary side ground end GND1, a secondary side ground end GND2, a synchronous rectification signal output end SYN, a sampling input end Vo, a first driving signal input end Vg1 and a second driving signal input end Vg 2;
the internal circuit includes: the circuit comprises a MOS tube Q1, a diode D1, a transformer TX1 and a sampling circuit unit 101; the sampling circuit unit 101 includes: MOS transistor Q2, capacitor C1;
the primary side connection relationship is as follows:
the same-name end of a primary winding of a transformer TX1 is connected with a direct-current power supply input end VCC, the different-name end of the primary winding of the transformer TX1 is simultaneously connected with the drain of an MOS tube Q1, the source of an MOS tube Q2 and a synchronous rectification signal input end BOS, the source of an MOS tube Q1 is connected with a primary ground end GND1, the grid of an MOS tube Q1 is connected with a first driving signal input end Vg1, the drain of the MOS tube Q2 is simultaneously connected with one end of a capacitor C1 and a sampling output end Vs, the other end of the capacitor C1 is connected with a primary ground end GND1, and the grid of an MOS tube Q2 is connected with a second driving;
the secondary side connection relation is as follows:
the different-name end of the secondary winding of the transformer TX1 is connected with the anode of the diode D1 and the synchronous rectification signal output end SYN at the same time, the same-name end of the secondary winding of the transformer TX1 is connected with the secondary ground end GND2, and the cathode of the diode D1 is connected with the sampling input end Vo.
Preferably, the switching power supply circuit having the synchronous rectification communication function is a flyback switching power supply circuit.
As an improvement of the technical scheme, the method is characterized in that: the circuit 431 also comprises a circuit 431, wherein the circuit 431 comprises a resistor R1, a resistor R2, a resistor R3 and a TL 431; the cathode of the diode D1 is connected to one end of the resistor R1 and the cathode of the TL431 at the same time, the other end of the resistor R1 is connected to the sampling input Vo and one end of the resistor R2 at the same time, the other end of the resistor R2 is connected to the reference voltage terminal of the TL431 and one end of the resistor R3 at the same time, and the anode of the TL431 and the other end of the resistor R3 are connected to the secondary ground terminal GND2 at the same time.
As an improvement of the technical scheme, the method is characterized in that: a compensation circuit is also included and is connected across the other terminal of resistor R2 and the cathode of TL431 for providing loop compensation to the feedback loop.
As a specific embodiment of the compensation circuit, the following features: the compensation circuit is composed of a capacitor C2.
As an equivalent alternative to the above-described modifications, it is characterized in that: also included is a resistor R4 connected between the cathode of diode D1 and the cathode of TL 431.
The specific working principle of the present invention will be analyzed and explained in the specific embodiments, which are not described herein. Compared with the prior art, the invention has the beneficial effects that:
1. the isolation transformer realizes two functions of synchronous rectification signal transmission and isolation voltage sampling, and has high utilization rate of devices, small occupied area of the board and low cost;
2. an isolation transformer is used for replacing an optical coupler, so that the optical coupler is free of strong attenuation of light, and the temperature drift is small;
3. the secondary side does not need 431 and peripheral circuits of the traditional scheme, the circuit structure is simplified, and the PCB layout space is saved.
Drawings
Fig. 1 is a schematic circuit diagram of a conventional synchronous rectification flyback switching power supply circuit;
FIG. 2 is a schematic circuit diagram of a first embodiment of the present invention;
fig. 2-1 is a schematic diagram of the application of the first embodiment of the present invention in a synchronous rectification flyback switching power circuit;
FIG. 2-2 is a waveform illustrating operation of the first embodiment of the present invention;
fig. 2-3 are schematic diagrams of the application of the first embodiment of the present invention in a synchronous rectification asymmetric half-bridge flyback switching power supply circuit;
FIG. 3 is a circuit schematic of a second embodiment of the present invention;
FIG. 4 is a schematic circuit diagram of a second embodiment in which the compensation circuit is a capacitor;
fig. 5 is a schematic circuit diagram of a third embodiment of the present invention.
Detailed Description
The invention of the application is that a switching power supply circuit with a synchronous rectification communication function is utilized, the power tube is fed with a narrow pulse to control the turn-off of the synchronous rectification tube, and an output voltage signal is fed back to the primary side, so that the problem of low utilization rate of a magnetic isolation transformer in the conventional synchronous rectification signal transmission is solved, a 431 circuit on the secondary side can be omitted, and the board distribution area is reduced. The sampling control circuit of the invention combines the synchronous rectification control and the isolation sampling function, improves the utilization rate of the transformer, has good temperature characteristic, small occupied area and low cost.
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
First embodiment
Referring to figure 2 which is a circuit schematic of a first embodiment of the invention,
the port includes: the synchronous rectification circuit comprises a direct-current power supply input end VCC, a sampling output end Vs, a synchronous rectification signal input end BOS, a primary side ground end GND1, a secondary side ground end GND2, a synchronous rectification signal output end SYN, a sampling input end Vo, a first driving signal input end Vg1 and a second driving signal input end Vg 2;
the internal circuit includes: the circuit comprises a MOS tube Q1, a diode D1, a transformer TX1 and a sampling circuit unit 101; the sampling circuit unit 101 includes: MOS transistor Q2, capacitor C1;
the primary side connection relationship is as follows:
the same-name end of a primary winding of a transformer TX1 is connected with a direct-current power supply input end VCC, the different-name end of the primary winding of the transformer TX1 is simultaneously connected with the drain of an MOS tube Q1, the source of an MOS tube Q2 and a synchronous rectification signal input end BOS, the source of an MOS tube Q1 is connected with a primary ground end GND1, the grid of an MOS tube Q1 is connected with a first driving signal input end Vg1, the drain of the MOS tube Q2 is simultaneously connected with one end of a capacitor C1 and a sampling output end Vs, the other end of the capacitor C1 is connected with a primary ground end GND1, and the grid of an MOS tube Q2 is connected with a second driving;
the secondary side connection relation is as follows:
the different-name end of the secondary winding of the transformer TX1 is connected with the anode of the diode D1 and the synchronous rectification signal output end SYN at the same time, the same-name end of the secondary winding of the transformer TX1 is connected with the secondary ground end GND2, and the cathode of the diode D1 is connected with the sampling input end Vo.
The functions of the ports of the embodiment are as follows:
dc power supply input VCC: providing direct-current voltage, so that when the drain electrode and the source electrode of the MOS transistor Q1 are conducted, energy flows through the primary winding of the transformer TX 1;
sampling output terminal Vs: outputting the voltage amplitude analog quantity sampled by the embodiment;
synchronous rectification signal input terminal BOS: receiving a pulse signal output by a primary side control IC BOS pin in a switching power supply circuit;
primary ground GND 1: providing a flow path for the input DC voltage and the backflow of the signal;
secondary ground GND 2: providing a flow path for energy coupled from the primary side to the secondary side;
synchronous rectification signal output end SYN: coupling a pulse signal received by a synchronous rectification signal input end BOS to a secondary side through a transformer TX1 and then outputting the pulse signal to a secondary side control IC SYN pin;
sampling input Vo: connecting a voltage point to be sampled;
first drive signal input terminal Vg 1: providing a driving signal for the MOS transistor Q1;
second drive signal input terminal Vg 2: and a driving signal is provided for the MOS transistor Q2.
Fig. 2-1 is an application schematic diagram of the first embodiment of the present invention in a synchronous rectification flyback switching power supply circuit, and since a sampling point is an output terminal of the synchronous rectification flyback switching power supply circuit, that is, a sampling input port is connected to the output terminal of the synchronous rectification flyback switching power supply circuit, the sampling point is represented by the same reference numeral Vo, pins of the primary side control IC and the secondary side control IC in fig. 2-1 also have such a connection relationship, and are also represented by the same reference numeral, and in addition, corresponding parameters also adopt english codes identical to the reference numerals.
The pin meanings of the primary side control IC and the secondary side control IC in the figure 2-1 are explained as follows:
VCC: a DC power supply input terminal;
GND 1: a primary side grounding end;
FB: the voltage feedback end is used for forming voltage closed-loop feedback;
BOS: outputting a pulse signal to a synchronous rectification signal input end BOS of the sampling control circuit, wherein the pulse signal can be positive or negative, and can be single pulse or multi-pulse;
vg 1: outputting a driving signal to a first driving signal input terminal Vg1 of the sampling control circuit;
vg 2: outputting a driving signal to a second driving signal input terminal Vg2 of the sampling control circuit;
GT 1: outputting a driving signal of a main power MOS tube Q4 of the flyback switching power supply circuit;
GT 2: outputting a driving signal of a synchronous rectifier tube Q3 of the flyback switching power supply circuit;
SYN: receiving a pulse signal output by a synchronous rectification signal output end SYN of the sampling control circuit, and controlling the on or off of a synchronous rectification tube Q3;
GND 2: a secondary side grounding end;
the meaning of each parameter related to this example is explained:
vg 1: a driving signal of the MOS transistor Q1;
vg 2: a driving signal of the MOS transistor Q2;
vd: the drain voltage of the MOS transistor Q1;
vcc: a direct current power supply input voltage;
vc: the body diode conduction voltage drop of the MOS transistor Q2;
vo: the switching power supply circuit outputs voltage;
vs: sampling a voltage;
n: and the primary side turn ratio and the secondary side turn ratio of the transformer TX 1.
The operation principle of the synchronous rectification flyback switching power supply circuit in fig. 2-1 is well known and will not be described herein.
The working principle of the sampling control circuit of the embodiment is described as follows:
referring to fig. 2-2, the working waveforms of the first embodiment of the present invention are shown, and the working process of this embodiment in one working cycle is as follows:
[t1-t2]in a time period, Vg1 is at a high level, the MOS tube Q1 is switched on, the transformer TX1 excites the excitation inductor to store energy, and the output end SYN of the synchronous rectification signal is a negative voltage;
[t2-t3]within a time period of t2When Vg1 is low level, MOS tube Q1 is turned off, diode D1 is turned on, Vd can induce the reflected voltage V of secondary side according to Lenz's lawd＝Vcc+nVoSimultaneously, line resistance, transformer leakage inductance and MOS transistor Q1 junction capacitance can generate RLC oscillation, so that V is converted intod＝Vs+VcAt this time, the body diode of MOS transistor Q2 is turned on, Vd voltage is clamped, and V is presentd＝Vcc+nVo+VcIn this stage, the output end SYN of the synchronous rectification signal is at a high level;
[t3-t4]within a time period of t3At the moment Vg2, Vg2 is high, MOS transistor Q2 starts to conduct, MOS transistor Q2 has small internal resistance, small current and small voltage drop, and voltage drop generated when MOS transistor Q2 and diode D1 conduct is ignored, and at this moment, V is approximately equal to Vd＝Vcc+nVoVd voltage is sampled to a capacitor C1 through a MOS tube Q2, and the voltage on the capacitor C1 is Vs＝Vd＝Vcc+nVoThe voltage is output to a voltage feedback pin FB of the primary side control IC to realize voltage closed loop feedback;
[t4-t5]in a time period, Vg2 is at a low level, the MOS transistor Q2 is turned off, the transformer TX1 releases energy to the output capacitor of the switching power supply circuit, the diode D1 is continuously turned on, and the output end SNY of the synchronous rectification signal is at a high level;
[t5end of cycle]After the energy of the transformer TX1 is released, the diode D1 is turned off, and the output end SYN of the synchronous rectification signal is at a low level;
due to the fact that3-t5]During the period, the SYN signal at the output end of the synchronous rectification signal is at a high level, and at other times, the SYN signal is at a low level, so that the secondary control IC can control the on/off of the synchronous rectification tube Q3 by using the signal. Therefore, by controlling the time of the primary side Vg1 signal, the on-off of the secondary side synchronous rectifier Q3 can be controlled. In practical application, the power supply circuit can be switched on or off according to actual needsDuring one working period, a plurality of Vg1 signals are sent out to control the synchronous rectifier tube.
As can be seen from the above description, the transformer TX1 in this solution transmits both the voltage signal and the synchronous rectification signal, so that device multiplexing is achieved, and this solution does not need 431 circuits on the secondary side, so that PCB area can be saved.
The switching power supply circuit applied in this embodiment may be other switching power supply circuits with synchronous rectification communication functions besides the synchronous rectification flyback switching power supply circuit shown in fig. 2-1, fig. 2-3 shows an application schematic diagram of the first embodiment of the present invention in a synchronous rectification asymmetric half-bridge flyback switching power supply circuit, and the primary side control IC further has a pin GT3 to output a driving signal of a main power MOS transistor Q5 of the flyback switching power supply circuit.
Second embodiment
Referring to fig. 3, a schematic circuit diagram of a second embodiment of the sampling control circuit of the present invention is shown, and the difference between this embodiment and the first embodiment is that compared with the first embodiment, the 431 circuit 102 including the compensation circuit is added, specifically, the 431 circuit 102 includes: the resistor R1, the resistor R2, the resistor R3, the TL431 and the compensation circuit have the connection relations that: the cathode of the diode D1 is simultaneously connected with one end of a resistor R1 and the cathode of the TL431, the other end of a resistor R1 is simultaneously connected with a sampling input Vo and one end of a resistor R2, the other end of the resistor R2 is simultaneously connected with a reference voltage end of the TL431 and one end of a resistor R3, the anode of the TL431 and the other end of the resistor R3 are simultaneously connected with a secondary side ground end GND2, a compensation circuit is bridged between the other end of the resistor R2 and the cathode of the TL431 and used for providing loop compensation for a feedback loop, and the loop compensation is used for adjusting the frequency characteristics of the loops of the primary side control IC and the secondary side control IC of the switching power supply so as to guarantee stable operation and transient response of the primary side control IC and the.
The description of the added parameters in this embodiment:
vcath: cathode voltage of TL 431.
The working principle of the present embodiment is different from that of the first embodiment in that the sampling control circuit does not sample the voltage Vo directly, but the voltage Vo is compared with the reference voltage terminal of the TL431 by the voltage dividing resistorThen outputting an error signal with the target voltage value, wherein the error signal is the cathode voltage Vcath of TL431, and the output signal is Vs＝Vcc+nVcathThe rest of the specific working principle is the same as that of the first embodiment, and is not described again. In the embodiment, because the voltage amplitude signal of the transmission signal of the transformer is changed into the relative error signal, the closed-loop control can be realized only by feeding back the change trend of the error to the primary side, the voltage stabilization precision of the circuit is controlled by 431, the required coupling degree of the transformer TX1 is reduced, and the design difficulty of the transformer is reduced.
The compensation circuit is implemented using a capacitor C2, see fig. 4, with a capacitor C2 connected across the other terminal of resistor R2 and the cathode of TL 431.
Third embodiment
Referring to fig. 5, a schematic circuit diagram of a third embodiment of the sampling control circuit according to the present invention, this embodiment is different from the second embodiment in that the sampling control circuit further includes a resistor R4 connected between the cathode of the diode D1 and the cathode of the TL431, and the voltage sampled by the sampling control circuit is not the voltage of the cathode of the TL431 to the GND2, but the voltage sampled by the resistor R4 connected in series with the cathode of the TL 431. The circuit can also realize closed-loop control.
The above are only preferred embodiments of the present patent, and it should be noted that the above preferred embodiments should not be considered as limiting the present patent. For those skilled in the art, it is obvious that several equivalent changes, modifications and decorations can be made without departing from the spirit and scope of the present invention, and these equivalent changes, modifications and decorations should be regarded as the protection scope of the present patent, which is not described herein by the embodiments, and the protection scope of the present patent shall be subject to the scope defined by the appended claims.

Claims (6)

1. A sampling control circuit is applied to a switching power supply circuit with a synchronous rectification communication function, and is characterized in that:
the port includes: the synchronous rectification circuit comprises a direct-current power supply input end VCC, a sampling output end Vs, a synchronous rectification signal input end BOS, a primary side ground end GND1, a secondary side ground end GND2, a synchronous rectification signal output end SYN, a sampling input end Vo, a first driving signal input end Vg1 and a second driving signal input end Vg 2;
the internal circuit includes: the circuit comprises a MOS tube Q1, a diode D1, a transformer TX1 and a sampling circuit unit 101; the sampling circuit unit 101 includes: MOS transistor Q2, capacitor C1;
the primary side connection relationship is as follows: the same-name end of a primary winding of a transformer TX1 is connected with a direct-current power supply input end VCC, the different-name end of the primary winding of the transformer TX1 is simultaneously connected with the drain of an MOS tube Q1, the source of an MOS tube Q2 and a synchronous rectification signal input end BOS, the source of an MOS tube Q1 is connected with a primary ground end GND1, the grid of an MOS tube Q1 is connected with a first driving signal input end Vg1, the drain of the MOS tube Q2 is simultaneously connected with one end of a capacitor C1 and a sampling output end Vs, the other end of the capacitor C1 is connected with a primary ground end GND1, and the grid of an MOS tube Q2 is connected with a second driving;
the secondary side connection relation is as follows: the different-name end of the secondary winding of the transformer TX1 is connected with the anode of the diode D1 and the synchronous rectification signal output end SYN at the same time, the same-name end of the secondary winding of the transformer TX1 is connected with the secondary ground end GND2, and the cathode of the diode D1 is connected with the sampling input end Vo.
2. The sampling control circuit of claim 1, wherein: the switching power supply circuit with the synchronous rectification communication function is a flyback switching power supply circuit.
3. The sampling control circuit of claim 1, wherein: the circuit 431 also comprises a circuit 431, wherein the circuit 431 comprises a resistor R1, a resistor R2, a resistor R3 and a TL 431; the cathode of the diode D1 is connected to one end of the resistor R1 and the cathode of the TL431 at the same time, the other end of the resistor R1 is connected to the sampling input Vo and one end of the resistor R2 at the same time, the other end of the resistor R2 is connected to the reference voltage terminal of the TL431 and one end of the resistor R3 at the same time, and the anode of the TL431 and the other end of the resistor R3 are connected to the secondary ground terminal GND2 at the same time.
4. The sampling control circuit of claim 3, wherein: a compensation circuit is also included and is connected across the other terminal of resistor R2 and the cathode of TL431 for providing loop compensation to the feedback loop.
5. The sampling control circuit of claim 4, wherein: the compensation circuit is a capacitor C2.
6. The sampling control circuit of any one of claims 3 to 5, wherein: also included is a resistor R4 connected between the cathode of diode D1 and the cathode of TL 431.
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CN102497105A (en) * 2011-12-02 2012-06-13 深圳市菱晟科技有限公司 Synchronous-rectification flyback switching power supply device and control method thereof
TWI635699B (en) * 2016-11-14 2018-09-11 立錡科技股份有限公司 Flyback power converter and synchronous rectification (sr) switch control circuit and power switch control circuit thereof
CN109995254B (en) * 2017-12-29 2020-12-29 东南大学 Method for improving dynamic performance of synchronous rectification primary side feedback flyback power supply
US10693384B1 (en) * 2019-06-26 2020-06-23 Cypress Semiconductor Corporation Accurate feed-forward sensing in flyback-transformer based secondary controller

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